Following are descriptions of the most common blood tests given to children with leukemia. If you have any questions about your child’s blood test results, ask the oncologist or nurse practitioner for a clear explanation.

Hemoglobin (Hgb)

Red blood cells contain Hgb, the molecules that carry oxygen and carbon dioxide in the blood. Measuring Hgb gives doctors an exact picture of the ability of the child’s blood to carry oxygen. Children may have low Hgb levels at diagnosis and during the intensive parts of treatment. This is because chemotherapy decreases the bone marrow’s ability to produce new red blood cells. Signs and symptoms of anemia—paleness, shortness of breath, fatigue—may occur if the Hgb gets very low.

Hematocrit (HCT)

The HCT is sometimes called the packed cell volume. The purpose of the HCT test is to determine the ratio of plasma (the clear liquid part of blood) to red blood cells in the blood. For this test, blood is drawn from a vein, a finger prick, or central catheter and is spun in a centrifuge to separate the red cells from the plasma. The HCT is the percentage of red blood cells in the blood. For example, if the child has an HCT of 30%, it means that 30% of the amount of blood drawn was red cells and the rest was plasma.

When a child is on chemotherapy, the bone marrow does not make many red cells and the HCT goes down. When the HCT is low, less oxygen is carried in the blood, so your child will have less energy. Your child may be given a transfusion of packed red cells if the HCT goes below 18 or 19%.

Red blood cell (RBC) count

RBCs are produced by the bone marrow continuously in healthy children and adults. These cells contain hemoglobin, which carries oxygen throughout the body. To determine the RBC count, an automated electronic device is used to count the number of red cells in a blood sample.

White blood cell (WBC) count

The total WBC count indicates the body’s ability to fight infection. Treatment for leukemia kills healthy white cells as well as diseased ones. It also impairs the ability of the bone marrow to make more WBCs. To determine the WBC count, an automated electronic device counts the number of white cells in a blood sample.

WBC differential

When a child has blood drawn for a complete blood count (CBC), one section of the lab report will state the total WBC and a “differential,” meaning that each type of white blood cell will be listed as a percentage of the total. For example, if the total WBC count is 1,500 mm³, the differential might appear as in the following table.

Absolute neutrophil count (ANC)

The ANC (also called the absolute granulocyte count or AGC) is a measure of the body’s ability to withstand infection. Generally, an ANC above 1,000 means the child’s infection-fighting ability is near normal.

To calculate the ANC, add the percentages of neutrophils (both segmented and band) and multiply by the total WBC count. Using the example above, the ANC is 49%+ 1%= 50%, and 50% of 1,500 (.50 x 1,500) = 750, so the ANC is 750.

Platelet count

Platelets are needed to repair the body and stop bleeding by forming clots. Because platelets are produced by bone marrow, platelet counts often decrease when a child or teen is on chemotherapy. Signs of low platelet counts are bruises and bleeding from the gums or nose. Platelet transfusions are sometimes given when the platelet count is lower than 20,000 or when there is bleeding. Platelets are counted by passing a blood sample through an electronic device.

Alanine aminotransferase (ALT)

ALT is also called serum glutamic pyruvic transaminase (SGPT). When doctors talk about liver functions, they are usually referring to blood tests that measure liver damage. If chemotherapy is causing liver damage, the liver cells release an enzyme called ALT into the blood serum. ALT levels can go up into the hundreds, or even thousands, in some children on chemotherapy. Each institution and protocol has different points at which chemotherapy drug dosages are decreased or stopped to allow the child’s liver to recover.

Aspartate aminotransferase (AST)

AST is also called serum glutamic oxaloacetic transaminase (SGOT). AST is an enzyme present in high concentrations in tissues with high metabolic activity, such as the liver. Severely damaged or killed cells release AST into the blood. The amount of AST in the blood is directly related to the amount of tissue damage. Therefore, if your child’s liver is being damaged by chemotherapy, the AST count can rise into the thousands. Viral infections or reactions to an anesthetic can also cause an elevated AST.

Bilirubin

The liver converts hemoglobin released from damaged RBCs into bilirubin. The liver then removes bilirubin from the blood and excretes it into bile, which is a fluid released into the small intestine to aid digestion. If too much bilirubin is present in the body, it causes a yellow color in the skin and whites of the eyes that is called jaundice.

The two types of bilirubin are indirect (also called unconjugated) and direct (also called conjugated). An increase in indirect bilirubin is seen when destruction of RBCs has occurred. An increase of direct bilirubin is seen when there is a dysfunction or blockage of the liver.

Blood urea nitrogen (BUN)

The BUN blood test is used to assess kidney function. It is also used to detect liver disease, dehydration, congestive heart failure, gastrointestinal bleeding, or shock. The test measures the amount of an end product of protein metabolism, called urea nitrogen, in the blood. For children with kidney or liver damage, BUN is often at abnormal levels.

Creatinine

Creatinine is a breakdown product of protein metabolism found in the urine and the blood. In children with leukemia, creatinine is measured to assess kidney function. An elevated blood creatinine level is often seen in children whose kidneys are not working well.

Glucose

The amount of glucose (sugar) in blood changes throughout the day, depending on when, what, and how much people eat, and whether they have exercised. A normal blood sugar level two hours after eating is less than 140 mg/dL. A normal fasting (no food for eight hours) blood glucose level is between 70 and 99 mg/dL.

Potassium

Potassium is important for the proper functioning of the nerves and muscles, particularly the heartbeat. Too much or too little potassium increases the chance of irregular heartbeats. Potassium levels can be altered by chemotherapy or other treatments for children with leukemia.

Calcium and magnesium

Calcium and magnesium are minerals that can be compared to the spark plugs in your car—they spark the chemical reactions in your body needed to make it function properly. Calcium and magnesium also help to develop and maintain the strength of bones. In addition, magnesium is needed for muscle development and nerve conduction throughout the body. Some chemotherapy drugs given to children with leukemia decrease the calcium and magnesium levels in the blood.